1. Field of the Invention
The present invention relates to a voltage regulator configured to keep the good accuracy of an output voltage even when a reference voltage circuit is influenced by a leakage current flowing at high temperature.
2. Description of the Related Art
A related-art voltage regulator is now described. FIG. 7 is a circuit diagram illustrating the related-art voltage regulator.
A differential amplifier circuit 104 compares a reference voltage (VREF) of a reference voltage circuit 103 and a feedback voltage (VFB) of a voltage divider circuit 106, and controls a gate voltage of an output transistor 105 so that the VREF and the VFB have the same value. When an output voltage of an output terminal 102 is represented by VOUT, the output voltage VOUT is obtained by the following expression.VOUT=(RS+RF)/RS×VREF  (1)where RF represents the resistance value of a resistor 121 and RS represents the resistance value of a resistor 122.
The reference voltage circuit 103 includes a depletion type NMOS transistor 131 and an NMOS transistor 132, and is controlled to improve the temperature characteristics of the reference voltage circuit 103 and keep the accuracy of the output voltage VOUT with respect to temperature (for example, see Japanese Patent Application Laid-open No. Hei 9-326469).
However, the related art has a problem in that, when the voltage regulator enters such a high temperature state that the NMOS transistor 132 and the depletion type NMOS transistor 131 that form the reference voltage circuit 103 cause a junction leakage current and a channel leakage current to flow, the VREF is decreased due to the influence of the leakage currents and the output voltage VOUT is decreased accordingly (see FIG. 6A). Further, there is another problem in that the accuracy of the output voltage VOUT cannot be kept within a certain range due to the influence of the leakage current flowing at high temperature.